During what time must all crew members fasten their seat belts according to procedures?

The correct response is that crew members must fasten their seat belts whenever the seatbelt sign is illuminated. This procedure is in place to ensure the safety and security of all crew members and passengers on board the aircraft. The seatbelt sign is activated during critical phases of flight, including turbulence, takeoff, and landing.

While "Brace for landing" is an important instruction for crew members, the requirement to wear seatbelts extends beyond that specific moment. It is crucial for crew members to be prepared for potential turbulence at any time and to remain securely in their seats when the seatbelt sign indicates it is necessary. This ensures the safety of the crew, who may be moving around the cabin, and helps to maintain a standard of preparedness for unexpected situations that could arise during flight.